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Background and Objective: Despite constituting one-third of suspected autoimmune encephalitis (AE) patients, antibody-negative cases without typical AE features are understudied. We aim to characterize the clinical phenotypes and long-term outcomes of "possible only" and "probable" AE cases., Methods: We conducted a retrospective analysis of adult patients evaluated at Mayo Clinic's Autoimmune Neurology Clinic (01/01/2006-12/31/2020), meeting diagnostic criteria for "possible only" or "probable but antibody-negative" AE, with ≥ 1 year of follow-up. All patients underwent neural antibody testing., Results: Among fifty-one patients, six had a change in diagnosis (non-autoimmune, 2) and were excluded from further analysis. Forty-five patients were analyzed [median age, 61 years (range 20-88); female, 21 (47%); median follow-up, 36 months (range 12-174)]. A nadir modified Rankin Scale (mRS) ≥ 3 was recorded in 41/45 (91%). CSF was inflammatory in 20/44 (45%) and MRI had encephalitic changes in 21/45 (47%). Unclassified neural-specific IgG staining on tissue-based assay was detected in five (11%). Two patients (4%) had paraneoplastic causation. Relapses (> 3 months from onset) were noted in 14 (31%). Memory dysfunction (69%), attention deficits (38%), and gait instability (29%) were the most frequent at the last follow-up. Most patients (76%) were independent at the last follow-up and only two required an assistive device to ambulate; 11 patients (24%) had poor neurological outcome (mRS ≥ 3). Higher mRS score and gait assistance requirement at 3 months were predictive of poor outcome (P ≤ 0.01)., Discussion: Despite significant disability at initial disease stages, most antibody-negative AE patients regain independent functioning. Early functional status and gait assistance requirements may predict long-term prognosis., Competing Interests: Declarations. Conflict of interest: Georgios Mangioris and Emma Orozco report no disclosures. Divyanshu Dubey has consulted for UCB, Immunovant, Argenx, Arialys and Astellas pharmaceuticals. All compensations for consulting activities are paid directly to Mayo Clinic. He is a named inventor on filed patent that relates to KLHL11 as marker of autoimmunity and germ cell tumor. He has patents pending for LUZP4-IgG, cavin-4-IgG and SKOR2 IgG as markers of neurological autoimmunity. He has received funding from the DOD (CA210208 & PR220430), David J. Tomassoni ALS Research Grant Program and UCB. Eoin P. Flanagan has served on advisory boards for Alexion, Genentech, Horizon Therapeutics and UCB. He has received research support from UCB. He has received speaker honoraria from Pharmacy Times. He received royalties from UpToDate. He is a site principal investigator in a randomized clinical trial of Rozanolixizumab for relapsing myelin oligodendrocyte glycoprotein antibody-associated disease run by UCB. He is a site principal investigator and a member of the steering committee for a clinical trial of satralizumab for relapsing myelin oligodendrocyte glycoprotein antibody-associated disease run by Roche/Genentech. He has received funding from the NIH (R01NS113828). He is a member of the medical advisory board of the MOG project. He is an editorial board member of Neurology, Neuroimmunology and Neuroinflammation, The Journal of the Neurological Sciences and Neuroimmunology Reports. A patent has been submitted on DACH1-IgG as a biomarker of paraneoplastic autoimmunity. Sean J. Pittock has received personal compensation for serving as a consultant for F. Hoffman-LaRoche AG, Genentech, Sage Therapeutics, Astellas and Arialis. He’s received personal compensation for serving on scientific advisory boards or data safety monitoring boards for F. Hoffman-LaRoche AG, Genentech, and UCB. His institution has received compensation for serving as a consultant for Astellas, Alexion/Astra Zeneca Rare Diseases, and Horizon/Amgen. All compensation is paid to Mayo Clinic. He has received research support from Alexion/Astra Zeneca Rare Diseases, Horizon/Amgen, F. Hoffman-LaRoche AG, Genentech and Adimmune. He has a patent, Patent# 8,889,102 (Application#12-678350, Neuromyelitis Optica Autoantibodies as a Marker for Neoplasia)—issued; a patent, Patent# 9,891,219B2 (Application#12-573942, Methods for Treating Neuromyelitis Optica (NMO) by Administration of Eculizumab to an individual that is Aquaporin-4 (AQP4)-IgG Autoantibody positive)-issued and from which he has received royalties. He is working as a consultant in the Mayo Clinic Neuroimmunology laboratory clinical service. He has patents issued for a variety of target antigens including MAP1B-IgGs, KLCHL11, SKOR2, and LUZP4 IgGs. Anastasia Zekeridou has patents submitted for Tenascin-R-IgG, PDE10A-IgG, CAMKV-IgG, and DACH1-IgG as biomarkers of paraneoplastic neurological autoimmunity. She has received research funding from Roche not relevant to this work and the Mayo Clinic Center for MS and Autoimmune Neurology. She’s consulted, without personal compensation, for Alexion Pharmaceuticals. Andrew McKeon reports research funding from National Institutes of Health (NIH: RO1NS126227, U01NS120901), patents issued for GFAP and MAP1B-IgGs and patents pending for CAMKV, PDE10A, Septins-5 and -7, and KLCHL11-IgGs, and has consulted for Janssen and Roche pharmaceuticals, without personal compensation. Ethical approval: This retrospective study was approved by the Mayo Clinic Institutional Review Board (IRB, 21-001297). Medical records of patients who consented to research review were included., (© 2024. Springer-Verlag GmbH Germany, part of Springer Nature.)

Immune-mediated cerebellar ataxias (IMCAs) represent a group of disorders in which the immune system targets mainly the cerebellum and related structures. We address fundamental questions on the diagnosis and immunological pathogenesis of IMCAs, as illuminated by recent advances in the field. Various types of IMCAs have been identified, including post-infectious cerebellitis, Miller Fisher syndrome, gluten ataxia, paraneoplastic cerebellar degeneration (PCD), opsoclonus and myoclonus syndrome, and anti-GAD ataxia. In some cases, identification of several well-characterized autoantibodies points to a specific etiology in IMCAs and leads to a firm diagnosis. In other cases, various autoantibodies have been reported, but their interpretation requires a careful consideration. Indeed, some autoantibodies have only been documented in a limited number of cases and the causal relationship is not established. In order to facilitate an early treatment and prevent irreversible lesions, new entities have been defined in recent years, such as primary autoimmune cerebellar ataxia (PACA) and latent autoimmune cerebellar ataxia (LACA). PACA is characterized by autoimmune features which do not align with traditional etiologies, while LACA corresponds to a prodromal stage. LACA does not imply the initiation of an immunotherapy but requires a close follow-up. Concurrently, accumulation of clinical data has led to intriguing hypotheses regarding the mechanisms of autoimmunity, such as a pathogenesis of autoimmunity against synapses (synaptopathies), and the vulnerability of the entire nervous system when the immunity targets ion channels and astrocytes. The development of PCD in patients treated with immune-checkpoint inhibitors suggests that molecular mimicry specifically determines the direction of autoimmunity, and that the strength of this response is modulated by co-signaling molecules that either enhance or dampen signals from the antigen-specific T cell receptor., (© 2024. Springer-Verlag GmbH Germany, part of Springer Nature.)

Antibody-mediated encephalitis defines a class of diseases wherein antibodies directed at cell-surface receptors are associated with behavioral and cognitive disturbances. One such recently described encephalitis is due to antibodies directed at alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR). This entity is exceptionally rare and its clinical phenotype incompletely described. We present findings from two cases of AMPAR encephalitis that exemplify variability in the disease spectrum, and summarize findings in published cases derived from a systematic literature review. When all patients are considered together, the presence of psychiatric symptoms at presentation portended a poor outcome and was associated with the presence of a tumor. Furthermore, we provide evidence to suggest that the topography of magnetic resonance imaging abnormalities in reported cases mirrors the distribution of AMPARs in the human brain. The potential for neurological improvement following immunomodulatory therapy together with the favorable outcome reported in most cases emphasizes the importance of testing for autoantibodies against neuronal cell-surface proteins, including AMPAR, in patients with clinical and neuroimaging findings suggestive of autoimmune encephalitis. Close attention to the clinical phenotype may inform the presence of malignancy and long-term prognosis.

The field of neuronal surface-directed antibody-mediated diseases of the central nervous system has dramatically expanded in the last few years and now forms an important cluster of treatable neurological conditions. In this review, we focus on three areas. First, we review the demographics, clinical features and treatment responses of these conditions. Second, we consider their pathophysiology and compare autoantibody mechanisms and their effects to genetic or pharmacological disruptions of the target antigens. Third, we discuss areas of controversy within the field, propose possible resolutions, and explore new directions for neuronal surface antibody-mediated diseases.

Chronic meningitis is an inflammation of the meninges with subacute onset and persisting cerebrospinal fluid (CSF) abnormalities lasting for at least one month. Several non-infectious and infectious etiologies are known to be causative. The wide range of different etiologies renders the approach to patients with this syndrome particularly difficult. There is no standardized diagnostic procedure, thus, taking an in depth history combined with a complete physical examination is mandatory in every patient.This review aims to present the current knowledge on etiology, neurological course of disease, diagnostic and therapeutic management steps of patients presenting with clinical signs and symptoms of chronic meningitis and meningoencephalitis. Still, the etiology of one third of patients remains unclear, reflecting the diagnostic challenge of this syndrome for each physician or neurologist, respectively. However, most patients with idiopathic chronic meningitis have a relatively good outcome.

The IgG molecule is the main component of IVIg. Commercial preparations of IVIg are derived from a pool of donors and subsequently, IVIg products contain smaller amounts of IgA and IgM antibodies as well as Th2 cytokines and cytokine antagonists that may also contribute to therapeutic effects. Numerous targets for IVIg include: T-cells, cytokines, immune cell trafficking, B-cells, complement and Fc-receptors. IVIg has been demonstrated to inactivate auto-reactive T-cells by competing for and interrupting their interaction with antigen presenting cells. The balance of cytokines also appears to be restored by IVIg, with studies showing that IVIg contains antibodies and antagonists to pro-inflammatory cytokines. In addition, IVIg is thought to interfere with and prevent the passage of auto-immune T-cells into the blood-nerve barrier. The effects of exogenous antibodies on B-cells have been well studied; IVIg is thought to down-regulate antibody production by B-cells, interfere with B-cell proliferation via a blockade of cell surface receptors and prevent the activation of certain subtypes of B-cell. In addition, IVIg can affect innate immunity by interrupting the steps in the complement activation cascade and blocking Fc-receptor mediated activity, which results in down-regulation of macrophage activity. In conclusion, IVIg has numerous modes of action, which culminate in the down-regulation of the immune response; many of which may be relevant to neuromuscular disorders and immune neuropathies.

A number of autoimmune disorders have been identified in which IVIg treatment may be beneficial. Evidence for the use of IVIg in inflammatory myopathies comes from controlled trials in dermatomyositis (DM) and sporadic-inclusion body myositis (s-IBM). In DM, muscle strength was increased and neuromuscular scores and skin rashes improved. Results for s-IBM have not been as encouraging as those observed for DM. Subsequently, IVIg should be recommended as a second-line therapy in DM and used for life-threatening dysphagia in s-IBM. Using an animal model of experimental autoimmune myasthenia gravis (MG), studies also indicate that IVIg can significantly improve clinical symptoms and affect pathogenic idiotypic antibodies. In human MG, studies indicate that IVIg exhibited equal efficacy compared to plasmapheresis. IVIg can therefore be recommended for use in an MG crisis or in lieu of plasmapheresis. The role of IVIg in the chronic management of MG has not been studied. IVIg has also been investigated in autoimmune CNS disorders. In a controlled study in patients with stiff person syndrome IVIg was effective, with improvements in the distribution of stiffness index and heightened sensitivity scores. For neurodegenerative diseases such as Alzheimer's disease, post-polio syndrome, pain, fibrosis, and autoimmune sleep disorders, some early promising results for the use of IVIg are emerging, but remain to be fully investigated. In conclusion, IVIg appears to be an effective treatment for a number of autoimmune disorders, however, optimal dosing and pharmacogenetic studies are necessary.

The Chronic Dysimmune neuropathies (CDN) are a clinically heterogeneous group of polyneuropathies united by their presumed immune mediated aetiology. At present such neuropathies are classified as Chronic Inflammatory Demyelinating Polyneuropathy (CIDP), Multifocal Motor Neuropathy (MMN) and the Neuropathies in association with serum Paraproteins (Paraproteinaemic Neuropathies). This classification fails to recognise other distinctive syndromes and is limited by heterogeneity within, and overlap between, subgroups. We have refined this clinical subclassification by a review of a consecutive series of 102 unselected patients with CDN referred to a single neurologist. We recognise 6 clinical subtypes of CDN: one sensory ataxic group; three motor-sensory subgroups (chronic motor sensory demyelinating neuropathy, subacute motor sensory demyelinating neuropathy and a multifocal motor sensory neuropathy); and two pure motor subgroups (symmetric pure motor demyelinating neuropathy and multifocal motor neuropathy). This subclassification allows distinct syndromes to be recognised and helps resolve problems of heterogeneity and overlap. Distinction between these subgroups is of immediate practical relevance to patient management. Although steroids are beneficial for most of the subgroups, this is not so for both of the pure motor syndromes which should be treated with intravenous immunoglobulin. Patients with chronic development of Motor Sensory Demyelinating Neuropathy respond less well to steroids than those with a subacute onset. An association was found between elderly patients with Subacute Motor Sensory Demyelinating Neuropathy and carcinomas. Within any clinical subgroup patients behave similarly regardless of the presence of associated paraproteins or nerve specific antibodies.